A belt-like gastric band for encircling the stomach to control morbid obesity is disclosed by Vincent in U.S. Pat. No. 5,601,604, incorporated herein by reference. The band comprises a belt that can be passed around the stomach and locked into an encircling position in order to create a stoma opening within the stomach. An adjustable portion of the band comprises an inflatable member which permits fine adjustment of the stoma opening after the stoma is created by locking the band in place.
The gastric banding procedure may involve placement of a calibrating apparatus in the stomach to position the stoma and size the pouch created above the stoma. The gastric band is fastened in position about the stomach to prevent slippage, usually by gastro-gastric sutures.
The stoma opening may be adjusted by injecting or withdrawing a fluid into or from an inflatable member, which is preferably coextensive with a portion of the inner stomach-contacting surface of the band. The means for injecting the fluid into the inflatable member usually comprises a fill port located beneath the skin that can be accessed extracorporeally by transdermal injection. Thus, following implantation, the gastric band can be adjusted to enlarge or reduce the stoma as required.
A potential disadvantage of prior art gastric bands is the difficulty in finely adjusting the stoma created by the implanted band. For example, the fill port located beneath the skin can be difficult to locate precisely. In addition, the fill procedure requires an invasive transdermal injection to adjust the band. Hence, repeated adjustments may be painful or worrisome to the patient. Moreover, exposure to x-rays may be required to facilitate location of the port. It would therefore be desirable to provide a band having an inflatable member that can be easily, precisely, and readily adjusted remotely, without the need to undergo an invasive procedure or radiographic exposure.
To address this problem, several prior art remote control gastric banding devices have been proposed. Klaiber et al. (U.S. Pat. No. 5,938,669) discloses a radio controlled gastric band adjusted by means of an electric pump and a balancing reservoir. Forsell (U.S. Pat. No. 6,210,347) discloses a remotely controlled and powered gastric band adjusted by a motorized mechanical or hydraulic means. Each of these proposed devices operates by pumping fluid to or from the gastric band. Unfortunately, because of their energy requirements, these devices pose problems for practical use. These devices are also not suitable for use with existing gastric banding systems, such as that disclosed by Vincent.
Recent developments in implantable drug delivery devices have shown that small, reliable, and energy-efficient implantable devices are feasible.
Drug delivery devices currently exist in which drugs are administered periodically or continuously to a patient having an implanted device by applying pressure from a pressurized reservoir and opening an outlet valve to allow a pressure differential to cause a flow of the drug. For example, Malamud et al. (U.S. Pat. No. 5,928,195) discloses a remotely controlled drug delivery device suitable for implantation in a body cavity. A pressurized gas chamber presses upon a drug storage chamber thereby administering a dose of the drug when a valve is remotely opened.
Similarly, Arzbaecher (U.S. Pat. No. 5,607,418) discloses an implantable drug apparatus having nested deformable chambers with the outer chamber being pressurized. The pressure from the outer pressurized chamber forces the drug from a reservoir chamber into an inner dispensing chamber. A remotely controlled valve is used to administer a dose of the drug from the dispensing chamber.
Further, Haller et al. (U.S. Pat. No. 6,203,523) discloses an implantable drug infusion device having a flow regulating mechanism that permits the flow rate to be independent of reservoir pressure. Some of the tradeoffs between “passive” (pressurized reservoir-based) devices and “active” (pump-based) devices are discussed in Haller, as follows.
Active drug or programmable infusion devices feature a pump or a metering system to deliver the drug into the patient's system. An example of such an active drug infusion device currently available is the Medtronic SynchroMed™ programmable pump. Such pumps typically include a drug reservoir, a peristaltic pump to pump out the drug from the reservoir, and a catheter port to transport the pumped out drug from the reservoir via the pump to a patient's anatomy. Such devices also typically include a battery to power the pump as well as an electronic module to control the flow rate of the pump. The Medtronic SynchroMed™ pump further includes an antenna to permit the remote programming of the pump. Needless to say, in view of these various components, the cost as well as the size of active drug infusion devices is greater than desired.
Passive drug infusion devices, in contrast, do not feature a pump, but rather rely upon a pressurized drug reservoir to deliver the drug. Thus such devices tend to be both smaller as well as cheaper as compared to active devices. An example of such a device includes the Medtronic IsoMed™ This device delivers the drug into the patient through the force provided by a pressurized reservoir. In particular, this reservoir is pressurized with a drug to between 20 to 40 psi (1.3 to 2.5 bar) and is used to deliver the drug into the patient's system. Typically the flow path of the drug from the reservoir to the patient includes a flow restrictor, which permits a constant flow rate. The flow rate, however, is only constant, if the pressure difference between reservoir and patient does not change. Factors that could impact this pressure difference include temperature, pressure-volume dependence of reservoir and altitude, among others. The selected pressure for the reservoir is thus typically quite high, so that absolute pressure changes only cause small and acceptable errors in flow rate. This also requires, however, the drug to be injected into the reservoir using still higher pressure. This is often a very difficult to achieve using a hand operated syringe.
The foregoing demonstrates a need for a practical, accurate and easy means of remotely adjusting an implanted gastric band.